A tunnel-type batch washing machine has an outer housing tube that is centered on a horizontal axis and that has an upstream intake end and a downstream output end. Provided inside this tube is a so-called washing screw having an axial succession of flights defining respective compartments inside the tube. A sleeve may be fixed to the screw between same and the tube. Normally clear water is introduced at the downstream end, and the tube is pitched slightly toward the upstream end so that this liquid will flow through it and the sleeve toward this upstream end.
In use the screw and sleeve are oscillated back and forth through less than 360.degree. and are periodically rotated in one direction only through more than 360.degree.. In this manner individual batches or loads of laundry or the like that are held in the individual compartments are agitated during the back-and-forth oscillation of the screw, and are advanced sequentially downstream from one compartment to the next during the rotation through more than one revolution. In this manner it is possible to wash or otherwise liquid-treat large quantities of articles while maintaining the articles in separate discrete batches.
The main disadvantage with such washers is that they do not clean very effectively. This is normally due to the inadequate agitation during oscillation of the screw, although this problem can be somewhat alleviated by forming the screw with a stepped washboard-type surface as described in the commonly owned and jointly filed application Ser. No. 168,459. Even with such expedients, it is frequently necessary to use extremely strong cleansing agents to obtain adequate results. Such agents frequently are so strong that they damage the article being cleaned. Furthermore it is difficult with such machines to maintain the water sufficiently hot, as even if the water is introduced at a very high temperature, it quickly cools down so that by the time the spent rinse water has reached the upstream washer zones it is relatively cool.